Advice on using 2-part foam

Does anyone have advice for working with SMALL amounts of 2-part foam? I have 3 things that I want to fill with foam. The volume I want to fill in each is 9.71 cubic inches. The foam can expand up to 20 times its original volume, so the original volume for each is .49 ci. That's 7.96 ml. Since it is 2-part foam, each part is only 3.98 ml.

How do you measure and mix such small amounts? It seems like a process that would be prone to error. If I'm trying for 8 mls of original liquid in the cup in which I am going to do the mixing, doesn't it seem like an ml or 2 could remain in the mixing cup when I do the pour? 2 mls out of 8 is a significant error, and then if I wanted to complete the casting, I'd be stuch trying to mix even smaller volumes!

I'm considering mixing the liquid for each of the 3 pieces and pouring a third into each, just so I can get the rations correct (about 12 mls each ingredient). But that also seems error prone, especially since after mixing, I guess the stuff can begin expanding very quickly. Measuring out 8 ml in each pour might not be easy if the stuff starts expanding before I've poured each part.

Any advice on how to use this foam is greatly appreciated.

Use some small oral syringes. They are cheep and very accurate. You can order them anywhere online. Get caps if you want to keep the stuff inside safe for your next project.

I eyeball it or use my triple beam gets close enough dont mix too much at a time and work quickly

Thanks guys.

This sounds like good advice for getting the mix ratio correct and measuring the two separate parts. But the main question I am asking is not how do I mix equal amounts of part A and part B. As long as I make it even, and I have a place to dump the extra as it foams up, I can mix extra. I have so much, I'm not concerned about waste. The main question is how do I measure out and pour a precise 8 ml of the mixed liquid into the part I'm filling? It just seems like a race against time when there is a need to be accurate.

I don't know how accurate one can be on a precised amount because there is always going to be some left in your mixing container. I always mix a little extra which results in the foam coming out or over the top of the area being foamed. After hardened the foam is trimmed back usually with a knife. Heat and humidity affect the amount the foam expands.

The foam doesn't expand equally as the resistance from the contact to the sides is greater than that of the air. This simply means the foam will dome like water in a glass graduated cylinder (not the same principle though). I don't recommend attempting to manipulate the foam to flatten it as this can result in breaking the trapped air leaving a hard mess. Just pour more in and cut off the excess and sand it down.

In an enclosed space, extra attention needs to be paid to prevent cavities from forming in the corners.

ThirstyBarbarian said:

Thanks guys.

The main question is how do I measure out and pour a precise 8 ml of the mixed liquid into the part I'm filling? It just seems like a race against time when there is a need to be accurate.

Click to expand...

Use a syringe,[just like injecting epoxy, ml's are marked on the side] I do it all the time, to reach areas in fin cans where pouring would make a mess, or where the open area I'm pouring is so narrow [1/4-1/2 in]

Pouring in a narrow space may clog the open area & you don't get liquid to the bottom.


Mix extremely fast in temps of 70 and above. You generally have 50 to 80 seconds before you are toast.Start timing when you start mixing . Mix till it looks like coffee with cream, no streaks, then ready to use.
Doing work at 65 or under really slows down the process & gives you more working time. So much so that sometimes you start to wonder if the stuff will ever begin to foam. Once you get it where you want, a hair dryer will easily warm things up again.

Put the bottles in the fridge for 20-30 minutes to cool down & retard the foaming action. This can lengthen the cure time to 5-10 minutes depending how cool you get it & the ambient temperature in the room.


I take the part you are working on is closed and no room for over expansion?

There are endless ways to use this stuff and to speed-up/slow down the foaming action.Just like epoxy it's all temperature dependent . Knowing that you can experiment a bit to get it done "your way". Lol:smile:



Most important thing to remember....Don't mess with it while curing, no wipe...smear...try to clean excess with rags. Wait till it get fully hardened then it will ..cut,sand, scrape...etc. quite easily.

Ps if the syringe has teeny tiny opening .... cut it off a bit to a more reasonable size. That would be as large as allowable for where you are injecting.By the way, yes you can re-use it. Pull the plunger out..... let everything cure overnight... then I use a drill bit, allen wrench .etc to push hardened foam residue out of syringe.

What are you trying to fill?

Thanks everyone.

I don't think I can set this up to foam over the top and trim off. But maybe someone can help me think this through so that it would work.

What I am trying to foam is the fin pods on my Mega Der Red Max with pods project. The pods are made from a length of BT60, with a rounded nose cone on the bottom, and a pointy one on top. I've already attached the BT60 to the fin edges, and I've attached the rounded nose cones to the bottoms. I've enlarged the holes in the bottom NC's so that the foam will get all the way down inside the NC. I want to be able to pour the foam inside the pod all the way down into the bottom NC, and have it rise up through the pod to fill most of it, but not go over the top. If it goes up over the top, it seems like it will be difficult to dig it out of the top of the BT60 enough so that I can insert the top nose cone.

The ideal thing would be to have the foam stop exactly at the shoulder length of the top NC. Then i could just drop in the top NC and glue it in place. I know that is impossible, so what do you think would be the best way to fill up to that level or cut back to that point? Is this stuff pretty easy to cut and dig out of a cavity? (This is 3 pound density.) Maybe if I masked the top inside of the BT down to the shoulder length, I could dig out the hardened excess down to that level and have a clean inside of the upper BT to glue in the top cone? Would that work? I guess it all depends on how easy the stuff is to cut and dig out once it is hardened.

Let me now your thoughts on this.

unless you can work REALLY fast, definitely mix separate batches, or you could end up like me.

https://www.rocketryforum.com/showthread.php?48184-DarkStar-Mini-Build-Thread&p=470718#post470718

https://www.rocketryforum.com/showthread.php?48184-DarkStar-Mini-Build-Thread&p=477860#post477860


There will be probably be some over expansion. Expect the foam to expand out of the area you are filling and tape off anything you don't want foam in. (Like the mouth of a motor mount tube if you are filling a fin can, for example.) Once the foam cures, it's really easy to cut and sand. (as long as you don't mess with it while it's still curing and cause the foam to collapse, then it's more of a pain to deal with.)

Edited to add details responding to Thirsty's last question (posted while I was looking for links to my old thread) Yes it is pretty easy to cut and sand once it has fully cured. Masking off the shoulder, letting the foam come up, curing, then carving out and pulling the tape might work. I'd test the process on a scrap tube first. You can also adjust the densities of some 2-part foams by mixing a small amount (a drop or two) of water to part A before mixing in part B. A less dense foam might be easier to work with in this application. (But it will expand MORE)

It seems like many people have had a misadventure with foam! I'm sure I'm about to have mine. I just don't want to RUIN anything.

I think I will try masking off the inside of the upper portion of the pod like I described and then masking the outside and making a big protective shield for everything I don't want excess foam to get on. Then I'll mix a little extra, pour it in, let it expand out the top, harden, and then cut and dig out everything from the upper part of the body tube. Hopefully the masking tape will make it a clean surface I can glue the top NC into.

I think I have some spare BT60 sized tubes I can set up for the same volume I am trying to fill, so I can do a practice run.

Thanks for the advice, everyone! I'll report back how it goes, unless I am trapped in foam.

Take pictures of the results! (or the aftermath) I'm curious to see how it works out.

Or have someone else take the pictures as you may have your hands busy with (or covered in) foam

rbelknap said:

Take pictures of the results! (or the aftermath) I'm curious to see how it works out.

Or have someone else take the pictures as you may have your hands busy with (or covered in) foam

Click to expand...

I'm going to end up like Stallone in Demolition Man...

Just as long as all restaurants don't end up Taco Bell, we'll be fine.

The foam project worked out perfectly.

I wanted to fill the pods on my MDRM-with-pods project so that the pods would be more rigid and better able to resist impact when the rocket landed on one of the pods. Here is the rocket, with the pods.



The bottom NC's were already glued in place, but the top NC's were not glued, so that they could be removed, and the foam could be poured in. This meant that I needed to keep the top part of the tube clean from foam so that the NC could be put back in later and glued into place. But I also needed to be sure the pod was completely filled up to the point where the shoulder would extend into the tube. I wanted the tube full right up to that point, but keep the tube clean above that point.



Here's a shot down into the pod tube. You can see I opened a hole in the bottom NC so that the foam would pour all the way into it and complete fill it. That bottom NC will take the brunt of landing, so I wanted it filled with foam. Also, there is a tab from the fin that is internally filleted to the pod tube. I figured foam will adhere to all of these surfaces and form a super solid bond. Also the pod tube is only regular BT60, so having it full of foam will help to prevent it from being crushed by impacts to the tube.




To check the expansion of the foam, I made a tube from TP rolls that is approximately the same volume as the pod to be filled.



I added a ring of masking tape inside the tube to the depth of the nosecone shoulder to see if that would protect the tube from foam. I figured the foam would rise up past that level, and after it solidified, I would just cut it out and remove the tape and have a clean surface down to the depth of the shoulder.




I built the tape up above the top of the tube and added a plastic bag for protection.



I mixed the foam and poured it in, and it foamed up and just barely extended out the top. Unfortunately I did not get a good picture of that! After it solidified, I cut the foam out of the top of the tube using an Exacto knife and removed the tape, leaving a flat surface at the depth of the NC shoulder and a clean surface inside the tube down to that level.



The top NC slid into the tube easily.



So the test worked perfectly!

The next post is actually doing this process on the rocket.

After the test, I foamed the pods on the actual rocket.

I prepared the pods with the tape inside the pod tubes to the depth of the NC shoulder, tape built up beyond the top of the tube, plastic bags for protection.



I mixed a bit more foam than what I used in the experiment and poured it into a pod. I just did each one separately, one at a time, after the previous one had solidified. Each one foamed up just out of the top, with a little bit spilling out.



I cut out the excess and removed the tape, just like in the experiment.



Then I glued the top NC's into place!



The foam definitely makes the lightweight materials of the pods a lot more solid. It adds between 1.5 and 2 ounces of extra weight, but definitely worth it for the strength it seems to add. We'll see how resilient it is to impact when I fly it.

Thanks for the advice everyone!

Foam is some pretty amazing stuff.

Capable of solving some complex and seemingly unsolvable problems.

Look at it with an open mind and amaze yourself with its endless uses!

Glad you took the time & figured it out..... now go out and do some more fantastic stuff with foam!

That's great Thirsty! I'm glad it worked out so well.

Just curious, did you also foam in the top nose pod cones? (I would have been tempted to foam those, too. but doubt it would be needed.)

rbelknap said:

That's great Thirsty! I'm glad it worked out so well.

Just curious, did you also foam in the top nose pod cones? (I would have been tempted to foam those, too. but doubt it would be needed.)

Click to expand...

I actually did not foam the pod cones. I don't think they will likely be subjected to as many impacts as other parts of the pods. I glued them in place with Gorilla Glue, which is kind of "foamy" too. That's why you see tape holding the NC's in place in the final picture --- I didn't want the glue to foam up too much and force the NC's out of position. It seem to work really well.

I may still get to foam a nosecone for this project. The rocket is turning out heavier than expected, and the stability probably needs to be corrected. I will probably need to add nose weight, and I am thinking about using BB's and pouring foam in on top. Or I could use BB's and Gorilla Glue. What do you think? Foam or Gorilla Glue?

rbelknap said:

That's great Thirsty! I'm glad it worked out so well.

Just curious, did you also foam in the top nose pod cones? (I would have been tempted to foam those, too. but doubt it would be needed.)

Click to expand...

Are you going to the LUNAR launch on Saturday? If so, you will probably get a chance to see this rocket. It would be great to meet you. SCrocketfan will also be there. He has given me some good advice on this rocket as well.

blackjack2564 said:

Foam is some pretty amazing stuff.

Capable of solving some complex and seemingly unsolvable problems.

Look at it with an open mind and amaze yourself with its endless uses!

Glad you took the time & figured it out..... now go out and do some more fantastic stuff with foam!

Click to expand...

Thanks! What do you think about using foam to secure nose weight?

My nephew wants to mix several gallons of foam ingredients together to see how big the blob will get...

ThirstyBarbarian said:

Thanks! What do you think about using foam to secure nose weight?

My nephew wants to mix several gallons of foam ingredients together to see how big the blob will get...

Click to expand...

you should check if Home Depot or other place has this fence foam, I purchase it and put the 2 liquid in separate jar, so I can use a little if I want.

https://can.sika.com/en/group/News/Sika_Post_Fix.html

they have it at Home Depot in Canada

https://www.homedepot.ca/product/post-fix/832491

ThirstyBarbarian said:

Thanks! What do you think about using foam to secure nose weight?

My nephew wants to mix several gallons of foam ingredients together to see how big the blob will get...

Click to expand...

I do it all the time.

Also foam loops of Kevlar in NC to have a recovery gear attachment point.

ThirstyBarbarian said:

Are you going to the LUNAR launch on Saturday? If so, you will probably get a chance to see this rocket. It would be great to meet you. SCrocketfan will also be there. He has given me some good advice on this rocket as well.

Click to expand...

I will be at the launch. I will probably be launching Harold the Purple Crayon, assuming I can find a motor for him. You can most likely find me at the Safety Check Table, or helping out at the pads. I may see if I can get Toe-Knee to hand off LCO for a while

ThirstyBarbarian said:

Thanks! What do you think about using foam to secure nose weight?

Click to expand...

That should work fine. The kevlar loop in foam trick works well too. In fact you can combine the two:



(just add more washers)